feat: display eligible member counts in admin pages

[mroderick]

Summary

This PR adds eligible member counts to admin pages, giving chapter organisers visibility into how many members can actually receive workshop invitations vs. total registered members.

Eligible members = members who have accepted Terms of Service AND are not banned/suspended.

Changes

Models

• Chapter#eligible_students - Returns students eligible for invitations
• Chapter#eligible_coaches - Returns coaches eligible for invitations
• Group#eligible_members - Returns members eligible for invitations

Admin Views

• Chapter show page: Shows "(X eligible, Y total)" for each group
• Group show page: Shows "(X eligible, Y total)" in members header

Motivation

From investigation in #2576, Brighton chapter discovered that 43% of registered members (653 out of 1,513) weren't receiving invitations because they hadn't accepted the Terms of Service. These were primarily legacy members who registered before TOC was required in February 2020.

Currently, organisers only see total member counts, giving them no visibility into this gap. This PR addresses that by showing both numbers.

How to Verify

Step 1: Setup

git checkout feature/add-eligible-methods-to-chapter
bundle install
rails db:migrate  # if needed

Step 2: Run Tests

# Run model specs
bundle exec rspec spec/models/chapter_spec.rb spec/models/group_spec.rb

# Expected: 17 examples, 0 failures

# Run feature specs
bundle exec rspec spec/features/admin/

# Expected: All tests pass

Step 3: Manual Verification

1. Start the Rails server:

   rails server

2. Create test data (in rails console):

   chapter = Chapter.first || Chapter.create!(name: 'Test Chapter', city: 'Test City', email: 'test@example.com', time_zone: 'London')
   
   # Create student group
   students = Group.find_or_create_by!(chapter: chapter, name: 'Students')
   
   # Create eligible member (accepted TOC, not banned)
   eligible = Member.create!(
     name: 'Eligible', surname: 'Student', email: 'eligible@example.com',
     about_you: 'Test', accepted_toc_at: Time.now,
     auth_services: [AuthService.new(provider: 'github', uid: '12345')]
   )
   Subscription.create!(member: eligible, group: students)
   
   # Create ineligible member (no TOC)
   ineligible = Member.create!(
     name: 'Ineligible', surname: 'Student', email: 'ineligible@example.com',
     about_you: 'Test', accepted_toc_at: nil,
     auth_services: [AuthService.new(provider: 'github', uid: '67890')]
   )
   Subscription.create!(member: ineligible, group: students)

3. Visit Admin Chapter Page:

   • Go to: http://localhost:3000/admin/chapters/[chapter-id]
   • Expected: See "Students (1 eligible, 2 total)" in the sidebar

4. Visit Admin Group Page:

   • Go to: http://localhost:3000/admin/groups/[group-id]
   • Expected: See "Members (1 eligible, 2 total)" in the header

Step 4: Edge Cases (Optional)

1. Create a banned member:

   banned = Member.create!(
     name: 'Banned', surname: 'Student', email: 'banned@example.com',
     about_you: 'Test', accepted_toc_at: Time.now,
     auth_services: [AuthService.new(provider: 'github', uid: '99999')]
   )
   Subscription.create!(member: banned, group: students)
   Ban.create!(
     member: banned,
     reason: 'Test ban',
     note: 'Test note',
     expires_at: 1.month.from_now,
     added_by: Member.first
   )

   • Refresh the pages
   • Expected: Eligible count stays at 1, total increases to 3

2. Test with no eligible members:

   • Set all members' accepted_toc_at to nil
   • Expected: See "Students (0 eligible, N total)"

Alternative: Using Fabricators

If you have test data set up, you can use Fabricators instead:

chapter = Fabricate(:chapter)
students = Fabricate(:group, chapter: chapter, name: 'Students')

# Eligible member
Fabricate(:member, groups: [students], accepted_toc_at: Time.now)

# Ineligible member (no TOC)
Fabricate(:member_without_toc, groups: [students])

# Banned member
Fabricate(:banned_member, groups: [students], accepted_toc_at: Time.now)

Checklist

• Added model methods with tests
• Updated admin views
• All tests pass
• No RuboCop offenses (on new code)
• Clean commit history

Related

• Investigation: Investigation: Brighton Chapter Invitation Numbers (April 15-16, 2026) #2576

[mroderick]

From verifying this locally: